Stability of the Pittsburgh sleep quality index and the epworth sleepiness questionnaires over 1 year in early middle-aged adults: The CARDIA study

Study Objectives: To describe the stability of the Pittsburgh Sleep Quality Index (PSQI) and the Epworth Sleepiness Scale (ESS) scores over 1 year among a population-based sample of black and white early middle-aged adults. Participants: More than 600 participants, aged 38 to 50 years, from the Chicago site of the Coronary Artery Risk Development in Young Adults (CARDIA) Study. Methods: The PSQI and ESS were completed twice, approximately 1 year apart, between 2003 and 2005. Seven PSQ1 4-level component scores, a global PSQI score, and the ESS scores were calculated, A PSQI global score greater than 5 was classified as poor quality sleep, and an ESS score greater than 10 was classified as high daytime sleepiness. Results: The mean +/- SD PSQI score was 5.7 +/- 3.1 in Year 1 and 5.9 +/- 3.1 in Year 2. The mean ESS score was 7.4 +/- 4.3 in Year 1 and 7.2 +/- 4.2 in Year 2. The Pearson correlation coefficient for the PSQI score in both years in the full sample was .68 and ranged from .54 among black men to .72 among black women. The Pearson correlation coefficient for the ESS score in both years in the full sample was .76 and ranged from .70 among black men to .80 among white men. In the full sample, 76% had the same PSQI dichotomous classification, and 85% had the same ESS dichotomous classification in both years. Conclusions: These results suggest that the PSQI and ESS are stable measures of sleep quality and sleepiness over the past year in early middle-aged adults.